DE2243682A1 - METALIZATION METHOD OF COMPONENTS - Google Patents

Description

Western Electric Company, Xncorpore-i ec Newby 2-9 Mew York, V = St. A. ■

Process for the metallization of components

The invention relates to the metallization of components, including integrated circuits, with a mask is used to delimit contact zones and connecting lines o In particular, the deposition of gold described on limited areas of a platinum surface

When manufacturing components, the electrode surfaces can be metallized by means of galvanic deposition a layer of gold on top of a previously deposited layer of platinum. »The platinum layer itself can be deposited on a substrate, for example made of titanium. One deposited directly on the platinum layer Mask made of an organic photoresist film is used to limit the formation of electrode connections and conductive path patterns with areas to be plated with gold are used. One that often occurs with galvanic deposition However, the problem is the imprecise limitation of the Gold electrode areas as a result of underplating; i.e. the gold is not limited to the areas bounded by the photoresist pattern, but also extends under the photoresist. This underplating occurs because of poor adhesion of the photoresist layer on the platinum layer on. .

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BAO OBfGiNAL

For metallizing integrated silicon circuit components is prescribed according to the state of the art (DT-PS 1 282 196) that for making connections to Silicon the entire surface is oxidized and that then Openings are etched through the silicon oxide layer into the underlying silicon layer. Next will Titanium is deposited on the entire surface because it is ultimately necessary to connect the component to external circuits required metals gold or silver do not adhere to silicon dioxide as well as titanium. Following the Deposition of titanium deposits a layer of platinum directly on the titanium. This is often done because gold, which is commonly used to connect the component to external circuits Metal tends to form brittle alloys with titanium. At this stage of the procedure, the entire Platinum surface can be masked with an organic photoresist using known photoresist techniques To limit connection and conductor tracks on the platinum surface. Gold is then only used on the exposed ones Platinum zones galvanically deposited. The remaining sections of the photoresist and platinum and titanium will be finally removed either by chemical dissolution or - in the case of platinum - by sputtering. (Since the gold layer is almost ten times as thick as the platinum

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layer is, - the sputtering does not remove any significant ■. borrowed part of the gold.)

However, a problem that often occurs here is the insufficient delimitation of the gold electrode areas because the photoresist film does not adhere well to the platinum. This, _r ; The problem only became important in the last few years when the. Reduction of the cause adjacent conductors to be short-circuited by extending the gold plating layer from one conductive surface to the next.

Suggestions were made to solve the problem » In the German patent application P 17 64 148 “2 is the deposition of a titanium layer on the platinum surface suggested «, This layer oxidizes in the environment r.tomperatures in air slightly, so that a thin layer of titanium oxide (TiOg) is formed. The photoresist adheres relatively well to the titanium oxide layer, so that at dor qni van i see the precipitation of gold - less

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Underplating of the photoresist occurs, as with direct application of the photoresist to the platinum surface. However Both the titanium and titanium dioxide layers must be etched before gold can be deposited.

Alternatively, GB-PS 1 211 657 discloses the deposition of a silicon layer on the platinum surface. This silicon layer is then oxidized, photoresist is applied to the silicon dioxide surface and also here the photoresist adheres well. However, in this case too, both the silicon and silicon dioxide layers must etched before the gold layer can be deposited.

According to the invention there is an improved adhesion of the mask Platinum and therefore a more precise delimitation of the electroplated gold layer is achieved by removing the platinum surface oxidized and the photoresist is deposited on the platinum oxide layer thus formed. The photoresist adheres well and no significant underplating occurs during gold electroplating. That exposed platinum oxide does not need to be in a separate place at the points where gold is to be deposited Step before the deposition of the gold must be removed, as any galvanic process involves deposition of gold, the exposed planetary oxide forced

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wise ^ metallic platinum! is reduced, before the,. ..-. ·. _; galvanic deposition - of the gold begins *. The removal of the P.hötölatkSi Plätinöxid-, the platinum and the titanium layer outside the areas where gold is down, can use in the field of metallization of components known effected \ f _e r s driving then easily ^ -. ". ·." ■ "■ -. ■ '

The platinum oxide layer is either anodic or deserted chemical oxidation in a strong oxidizing agent formed »For reasons of easier manufacture anodic oxidation preferred

It is apparent to the person skilled in the art that the inventive Concept for the metallization of a great variety .Different Components, including integrated circuits, Capacitors and resistors are applicable '. '

The invention is in the following description with reference to FIG Drawing explained in more detail, namely show:

Pig. 1 - 6 in section a section of one here

as a semiconductor chip having a transistor trained component, which is used to form contacts and interconnects is treated in the manner according to the invention *

1 shows example ^{1 of} a semiconductor component in which the body 10 is a section of a semiconductor wafer,

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BATH ORIGINAL

from which a number of semiconductor components are made

will. The conductive type zones 12 and 13 representing the base and the emitter have been produced by previous method steps using known masking and diffusion methods. These zones are from Grenzbzw. Transition layers 14 and 15 limited. A masking layer 16 made of silicon dioxide (SiO ₂ ) is formed on the surface of the body in order to delimit the contact zones for producing electrodes on the p-conducting base zone 12 and the η-conducting emitter zone 13.

The following description of the metallization process essentially agrees with the German mentioned above U.S. Patent 1,282,196, but with the modification according to the invention match. The purity of all the metals used corresponds to the normal commercial ones Practice.

As shown in FIG. 2, a layer 17 of titanium (about 0.15 to 0.3 µm) is deposited on the entire surface of the body Io, which layer forms an adhesive bond with the oxide layer 16. Following the precipitation of the titanium layer 17, a second metallic layer 18 made of platinum (approximately 0.15 to 0.3 μm ) is deposited over the entire surface. Both the precipitation of the titanium and the platinum is carried out in a suitable manner by means of known vacuum deposition processes, e.g. by cathodic

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dic atomization or evaporation using an electron beam carried out.

According to the invention, the platinum layer 18 is now oxidized differently from the prior art, so that. those in Fig. 3 Layer 19 shown is formed from platinum oxide. The Oxi-. dation can take place anodically in a large number of known platinum oxidizing solutions., Aqueous sulfuric acid is one such usable solution, for example. The oxide layer is described in detail as follows is formed on the entire platinum surface by applying either a voltage of 0.8 to 1.6 V for at least 10 seconds or a current density of 0.1 to 10 mA per qcm is applied until at least 0.8 V is reached. Alternatively the oxidation can be carried out chemically in a number of strong chemical oxidizing agents. Concentrated (70% by volume) hot (at least 70 C) nitric acid (HIJOo) is one such useful oxidizer.

The body 10 is then made to operate on known procedures coming back, prepared for the raising of a Photoresist mask. In Fig. 4, the photoresist mask 20 is on the surface of the platinum oxide layer 19 is formed. The mask 20 defines the pattern of the final metallic contacts.

From Fig. 5 it can be seen that gold contacts and connections 1 (approx. 1 - 2 iirn) are formed by galvanic Niodorschlagung. The galvanic IJiodorr.chl aqunq of gold au I

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BATH ORIGINAL

the platinum layer 18 takes place in the unmasked sections in which the platinum oxide layer 19 is exposed. A separate operation to remove the exposed
Platinoxidschxcht 19 before the galvanic deposition
of the gold is not required because the exposed
Platinum oxide in the gold plating solution is added electrochemically
metallic platinum is reduced before the precipitation of gold begins. The existing platinum oxide layer 19, which is still masked by the photoresist film 20, forms during
this galvanic deposition a surface on
which the photoresist film adheres well. The penetration of the deposited gold under the photoresist film 20 is therefore essentially prevented, thereby avoiding, for example, the possibility of short circuits.

For the galvanic deposition of gold on the exposed platinum oxide areas, all known
Deposition baths can be used. For example, were
Citrate, phosphate and modified cyanide baths used with success. A two-stage mechanism is observed in gold precipitation: (a) the exposed platinum oxide is first reduced to metallic platinum and (b) the gold is then electrodeposited on the platinum thus formed. As in I''ig. 6, the photoresist layer 20 and the layers of platinum oxide and platinum 1B, as well as the titanium layer 17 outside of the FIG

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gold-plated areas removed · The photoresist layer 20 is made using conventional, commercially available solvents removes »Pa platinum oxide, removed by methanol, the component can be rinsed in methanol »· The next step is the platinum layer together with the. all remaining platinum oxide removed in a suitable manner by back-sputtering. The gold layer is not significantly attacked because of its greater thickness. The titanium layer is then.by using a chemical etchant, for example, an aqueous solution of sulfuric acid and hydrofluoric acid ' removed.

It should be noted that the invention is directed to the broad class of devices described, including semiconductor devices, capacitors, resistors, and the like, in which poor adhesion of the photoresist layer to platinum raises the potential problem of poor delineation of contact areas as a result of underplating gold evokes. That; Although current interest is directed to the metallization of semiconductor surfaces ( e.g. silicon, germanium, IL- EL ·.! compound semiconductors), other surfaces can also advantageously be metallized in the manner according to the invention, namely insulators (e.g. silicon dioxide, silicon nitride, tantalum oxide, Tantalum nitride, aluminum oxide).

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Oxidation of platinum

Platinum can be oxidized using two methods: anodic and chemical. In anodic oxidation, the voltage is the critical parameter that must be controlled while in chemical oxidation the critical parameter is the oxidation potential.

a. Anodic oxidation

During the anodic oxidation of platinum, a layer of adsorbed oxygen is created on the surface of the platinum educated. It is not entirely certain whether the adsorbed oxygen layer reacts chemically and a platinum oxide layer forms or whether it is only physically adsorbed on the platinum surface, but it was found that oxygen begins to adsorb at anodic polarization at around 0.8 V (see James P. Hoare, The Electrochemistry of Oxygen, Interscience Publishers, New York (1968), pages 39-41.) In any case, the resulting stable layer of adsorbed oxygen creates a surface on which an organic photoresist is sufficiently adhered to cause underplating to prevent during the galvanic deposition of gold. This layer is referred to below as the platinum oxide layer designated.

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According to the invention, platinum is anodized with at least 0.8 V. that this tension is reached. The conditions of the voltage potential, the duration and the current density are chosen so that the formation of a complete oxide layer is ensured within a reasonable period of time 1.6 volts higher oxides, for example ,, _o PtO are formed which are undesirable because they are more difficult prior to gold plating to remove .are.

It may be necessary during the anodization Control current density rather than voltage. In these In some cases, the same voltage limits described above occur. When the anodizing current density is too low the platinum oxide layer is not formed within a reasonable period of time; while again higher oxides when the current density is too high. A suitable range of current density for the practice of the invention is given at 0.1 to Io mA / cm. This range ensures that the minimum voltage of 0.8 V is within a few Seconds is reached.

BATH ORIGINAL

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It takes at least 10 seconds at about 0.8V to get one to form a sufficient layer of oxide which meets the requirements of the invention. It is assumed that any additional treatment time is used to diffuse oxygen into the platinum to form a solid solution of platinum oxygen to form. Such extra treatment time is. advantageous because it ensures improved adhesion of the photoresist layer. One too long Treatment duration, however, leads to unnecessary consumption of time due to excessive diffusion of oxygen into the Platinum layer. One acceptable for the practice of the invention The duration is therefore on the order of a few minutes and the practical maximum of the treatment duration is 10 minutes.

Aqueous electrolyte solutions that generate oxygen at the anode and do not themselves oxidize before the formation of the oxide layer must be used when platinum is anodized. Examples of such solutions include sulfuric acid (H-SO.), Potassium hydroxide (KOH) and perchlorate salts (ClO ₄ ").

For a more complete discussion of the anodization of platinum, those skilled in the art are referred to the one cited above Brochure Ie by Hoare, (especially pages 13-46) .

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bo chemical oxidation

The usual known strong oxidizing agents can
can also be used to form the platinum oxide layer according to the invention * Such oxidizing agents must have an oxidation potential of at least -o.8o V relative
for the standard hydrogen half-cell reaction:

H ₂ = 2H ⁺ + 20 ~ (0.00 V).

Examples of oxidizing agents useful in the practice of the invention are

(1) 'Nitric acid (HNO ₃ ):

W ₂ O ₄ + 2H ₂ O = 2NO ₃ "+ 4H ⁺ + 2e" ^ (-0.80V)

or

HNO ₂ + H ₂ O = NO ₃ "* + 3H ⁺ 2e" (-0.94 V)

(2) Parchloric acid. (HClO ₄ ):

C1O ₃ ~ + H ₃ O = ClO ₄ "+ 2H ⁺ + 2e ~ (-1.19 V)

(3) Chromic acid (HpCrÖ.) And acidic solutions of potassium dichromate (K ₂ Cr ₂ O ₇ ):

2Cr ³⁺ + '7H ^ O = Cr.0 " ² " + 14H ⁺ + 6e ~ ^ ¹ ' ^{33 V)}

(4) acidic solutions of cerium sulfate (Ce (SO ₄ )):

Ce ³⁺ = Ce ⁴⁺ ₊ β "" ^ ^{1 '61 V)}

These values are from the work of Wendell M, Latimer, "Oxidation Potentials, 2" Edition, Prentice-Hall, Inc., Mew York (1952) " taken.

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These oxidizers work best when used at elevated temperatures. Should be platinum be immersed for at least 10 seconds. Longer times, e.g. 5 minutes, will result in the formation of a relative thick, reproducible platinum oxide layer is recommended.

Chemical oxidizers weaker than those listed above are, for example 30% hydrogen peroxide (HO-) do not lead to a useful one Platinum oxide layer to which the photoresist adheres sufficiently for the purposes of the invention.

Examples

a. A number of silicon chips with integrated Circuits were metallized in the manner according to the invention. Before the electroplating of gold on the platinum areas delimited by a photoresist pattern, the total platinum surface on each wafer to a final voltage of 1.6 V for a period of 5 minutes a current density of 0.2 mA / cm in normal sulfuric acid (IN HpSO) anodized.

Following the anodization of the platinum layer, the samples were rinsed in distilled water and coated with photoresist coated. The patterns were then matched with other patterns

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compared that according to the "known method according to the German Patent 1,282,196. Microscopic examination showed that the samples were also adherent anodized platinum was vastly improved. This was established by observing that for the same Gold deposition time for both sets of patterns, the underplating of gold under the photoresist for the patterns with anodized platinum was more than 50% lower.

b. The comparison of discs that are usually concentrated (70 vol.%) In heated (70 C) nitric acid for a Period of 5 minutes had been oxidized, with prepared according to the method according to German Patent 1,282,196 Slice produced similar results as above.

These results do not necessarily mean that the distance between electrode surfaces, which was previously about ο, οΐδ cm, can now be reduced by 50% , but the results show that there is a considerably lower risk of the electrode surfaces short-circuited by underplating will.

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Claims (6)

2243602 Patent claims e J method for producing a conductive electrode pattern, in which a photoresist masking layer is deposited on a platinum surface, parts of the photoresist masking layer for delimiting the conductive electrode pattern are removed and a gold layer is deposited on the platinum surface, characterized in that before the deposition of the photoresist masking layer the platinum surface is oxidized to form an oxygen-containing layer. 2. The method according to claim 1, characterized in that the oxidation lasts at least 10 seconds Anodization is carried out at a voltage of 0.8 to 1.6 V, the maximum voltage achieved being 1.6 V. is. 3. The method according to claim 2, characterized in that it is assumed that a voltage is less than that Minimum voltage of 0.8V is. 4. The method according to claim 3, characterized in that the anodization at an essentially constant current 2 density in the range from 0.1 to Io mA / cm is carried out. 309811/0838 5. The method according to any one of the preceding claims, characterized in that the platinum layer in one aqueous electrolyte is anodized. 6. The method according to claim 1, characterized in that the platinum layer in a chemical solution with a Oxidation potential of at least -o.8o V relative to the standard hydrogen half-cell reaction chemically oxidized will. 3098 11/08 3 8 BAD ORiGlNAU